This invention relates an apparatus and method for the installation of reinforced thermoplastic liners in pipelines, whether during the initial manufacturing of the pipeline, or in later renovation, upgrade or repair. In either case, the useful life of the pipeline is increased by the added burst strength of the liner and the corrosion protection afforded by the liner. To protect against damage to existing pipelines, corrosion resistant thermoplastic liners have been used to eliminate the need for excavating and replacing pipeline, which can be very costly.
The use of thermoplastic liners for protecting the interior of a pipeline has been disclosed in numerous references beginning with French Patent, 81 07346 (Laurent) and pipelining processes are further exemplified in U.S. Pat. Nos. 4,496,449; 4,394,202; 4,207,130; 4,985,196; and 3,429,954. However, these processes have proven to be only somewhat successful in relatively low-pressure pipelines with application in existing pipelines of no more than one to two miles in length.
In the past, essentially two types of liners for pipelines, loose fitting liners and tight fitting liners, were used. A loose fitting liner has been described as one that contains the pressure of the fluid or gas in the liner. A tight fitting liner is flush against and tightly engaged with the interior wall of the pipeline. The tight fitting liner is physically supported by the pipeline and so may depend on the strength of the pipeline to contain the pressure of the fluid or gas in the pipeline. Tight fitting liners offer certain advantages over loose fitting liners in that they may be less expensive, they do not have to bear significant loads, and they maintain the greatest possible inside diameter. Several methods of installing tight fitting liners are described in U.S. Pat. Nos. 5,072,622; 3,856,905; 3,959,424; and 3,462,825.
Unfortunately, there are problems with tight fitting liners. Although a tight fitting liner protects the interior of the pipeline from corrosion it does not protect the exterior of the pipeline. Corrosion damage may weaken the physical strength of the pipeline to the point where it is unable to bear the pressure within and cause leakage. Since the traditional tight fitting liner depends on the strength of the pipeline to contain the pressure of the fluid or gas in the pipeline, if the pipeline fails, the liner will fail. Failure of the liner and pipe will result in significant replacement cost and may be catastrophic to the environment depending on the nature of the substance contained in the pipeline.
Thus, repairing an existing pipeline by installing a liner as heretofore available does not solve all the problems associated with pipelines. These problems have been addressed by designing a liner with multi layers with sufficient strength to contain the pressure of the pipeline within which the liner is fitted and by incorporating leak detection and stress monitoring systems in the liner as disclosed in U.S. Pat. No. 5,551,484 (Charboneau). An alternative leak detection system for a tight fitting liner is disclosed in U.S. Pat. No. 5,072,622 (Roach, Whitehead) as well as the use of annular channels as disclosed in U.S. Pat. No. 6,220,079 (Taylor, Roach).
Even after the problems of burst strength and monitoring were addressed, there was another problem. Typically most processes for insertion of a liner in a pipeline involve the step of deforming or temporarily folding the liner into a cross section smaller than the receiving pipeline so that the liner might be drawn or pulled through the pipeline and eventually restored to its full cylindrical cross section and tightly fitting within the pipeline as disclosed in U.S. Pat. Nos. 5,395,472, 5,810,053 and 5,861,116 (Mandich). It can be seen that the length of liner, which could be installed intact, was limited by the longitudinal strength of the liner itself. In many oil and gas pipelines, particularly offshore where the length of the pipeline may exceed several miles, the installation of high burst strength tight fitting liners was impossible.